Most belt retractors currently being used in motor vehicle occupant safety restraint belt systems are of the so-called emergency-locking type in which the belt is automatically locked against withdrawal in the event of a collision or an abrupt stop but is otherwise free to be withdrawn from the retractor so that the occupant is able to lean forward. Some emergency-locking retractors have a mechanism that locks the belt reel against rotation in the unwinding direction in response to a sudden withdrawal of the belt, i.e. acceleration of the belt itself, which occurs when the occupant is thrown forward in a collision. Others have an inertia-responsive device for locking the belt reel when the vehicle is relatively abruptly accelerated--or, more accurately, when an inertia-responsive device associated with the retractor detects such acceleration of the vehicle. So-called double-safety retractors have a mechanism which responds to both rapid pull-out of the belt and acceleration of the vehicle. (Throughout this specification, the term acceleration is used in the broad sense of a change in velocity in any direction and includes what is sometimes, in every day parlance, referred to as deceleration.)
A large number of inertia-responsive actuating devices for use in emergency-locking retractors have been proposed. In general, the presently known inertia-responsive devices fall into three general types. First is the type which uses a pendulum to detect acceleration of the vehicle. Most of the pendulum-type inertia-responsive devices include a generally horizontal support arm affixed to the retractor frame and a pendulum having a cap-like head portion that is supported on the support arm, a stem hanging from the underside of the cap portion and extending down through a hole in the support arm and a mass at the lower end of the stem. When the retractor is accelerated in any direction, the pendulum tilts relative to the support arm, and the cap acts on some sort of a lever or other motion-transmitting element which in turn operates on a mechanism which ultimately locks the reel against rotation. Examples of retractors having pendulum-type inertia-responsive devices are found in U.S. Pat. Nos. 3,343,765, 3,930,622, 3,991,953 and 4,053,117, the last two of which are owned by the assignee of the present invention.
A second general type of inertia-responsive device comprises a support and a mass which rests on the support, normally in a stable upright position, tilts on the base in the event of acceleration of the base relative to the mass, and operates on a motion-transmitting device, such as a pawl which engages ratchet teeth on a ratchet wheel affixed to the belt reel. Two representative examples of this type of inertia-responsive device are found in U.S. Pat. Nos. 3,758,044 and 3,901,459.
The third type of inertia-responsive device in emergency-locking retractors relies upon rolling motion of a spherical mass on a support and a lever or some other output element which the mass moves and which actuates a locking mechanism associated with the belt reel. The following patents describe and illustrate inertia-responsive devices of this rolling mass category.
Proctor U.S. Pat. No. 3,237,729--the spherical mass rolls in a dish-shaped support and moves a lever located above it upwardly whenever the mass rolls out of the center of the support. PA1 Fiala U.S. Pat. No. 3,741,494--the spherical mass rolls on a horizontal support and works against a downwardly concave cam portion of a lever such that when the mass rolls from a central position under the cam, the lever is lifted up. PA1 Hayashi U.S. Pat. No. 3,770,224--a spherical mass retained in a box on a slidable arm rolls in a dish-shaped support, and a dish-like output cam on the slidable arm moves an actuating pin when the mass rolls from the center of the support. PA1 Stoffel U.S. Pat. No. 3,819,126--a sphere rolls in a dish-like support and normally holds a pawl in a position out of engagement with a ratchet wheel; the pawl has a pin which extends into a hole on the support and on which the ball normally rests but which is disengaged to allow the pawl to pivot when the ball rolls out of the center of the support.
Other examples of rolling mass devices are described and shown in Levasseur U.S. Pat. No. 3,921,931 and Fohl U.S. Pat. No. 4,050,644.
Many of the known inertia-responsive devices are of relatively complicated construction and require a large number of components and intricate assembly procedures; they are often costly to make and not always reliable. Some of the devices require large movements of the inertial mass to obtain the desired motion for transmission to the locking mechanism and thus take up valuable space and increase the size of the retractor, an important disadvantage in view of the current popularity and, indeed, economic necessity of small motor vehicles. Some designs of these devices are functionally inadequate insofar as they are sensitive to friction between the inertial mass and the lever, pawl or other output device or between components of an actuating linkage upon which the mass acts.